my phone still running super good and fast but the fast battery drain is stressing me out..i know probably this is a dumb question, but, there's some way to increase the battery capacity? it's possible to replace the battery with a bigger capacity one?
thank you in advance

no the only phone able to do that was the 5c using the 5s batt. i would check your tweaks (disable all of them with i cleaner) and get the batt life app that has the thirty min drainage test with them diabled then reenable one by one over course of day. some un updated tweaks have caused issues when paired with others and continuously have a function looping for no reason. a in privacy >diagnostica you can find evidence sometimes and allow you to narrow down which process is doing it and the. narrow tweaks specific to that one to check and make sure to check standby and active times in batt>settings to make sure your phone is sleeping when screen off and not awake with processes running, if its an app store app backup data using app manager and reinstall fresh, common problem since ios 11 dropped for updates to cause funny bugs in ios10 and below. also if you are pre ios 10 check your cycles your batt might be just getting old. good luck mine had an issue with a cellular settings tweak

My iPhone's battery was gone more than a year ago. I had to charge my phone 4 times a day at least. I used to carry a heavy power bank with me. Then i tried to replace the battery but the issue wasn't resolved. Finally, I changed the battery IC and now it's performing pretty well. I don't have to carry around any power bank now.